1. Technical Field
Embodiments of the present disclosure relate to control of an internal combustion engine using multiple sparks during a single combustion cycle.
2. Background
Various strategies are used to increase power density and downsize engines, i.e. provide smaller, lighter engines with power equal to or greater than more conventional larger and heavier engines. For example, lean air/fuel ratio operation, and cooled external exhaust gas recirculation (EGR) on boosted (turbocharged or supercharged) engines may be used to increase power density. Typically, these smaller engines operate at higher loads where pumping losses are reduced to further improve fuel economy. However, combustible mixtures supplied to the engine cylinders with high levels of dilution and lean air/fuel ratios are more difficult to ignite and to achieve complete combustion. In addition, high turbulence and high BMEP combustion conditions may lead to spark blowout.
Previous strategies for improving combustion have included increasing ignition energy by using larger spark plug gaps, raising the ignition coil output, and/or sparking multiple times. While these approaches may be suitable for some applications, increased ignition energy and/or unnecessary restriking may lead to premature spark plug wear and gap erosion resulting in associated combustion performance degradation, which may adversely impact fuel efficiency, drivability, and/or feedgas emissions.
Transient events, which may occur in response to a change in driver demand, such as an increase or decrease in accelerator pedal position, and/or in response to changing engine or ambient conditions, such as during engine warm-up, for example, may also lead to operating conditions with a dilute air/fuel charge. In port-injected engine applications, evaporation rate of the fuel puddle in the intake port is affected by differences in intake manifold filling and intake manifold pressure during increases and decreases in accelerator pedal/throttle valve positions, often referred to as tip-ins and tip-outs, respectively. Uncompensated air/fuel control would result in leaner than desired air/fuel ratios during tip-ins, and richer than desired air/fuel ratios during tip-outs. As such, the engine control strategy may increase fuel delivery to the engine for a period of time based on an empirically determined time constant established during engine development for the period of increased torque demand during a tip-in. Similarly, another empirically determined time constant may be applied by the engine control strategy to decrease fuel delivery for a period of time during decreased torque demand during a tip-out. This transient fuel compensation strategy is often performed in open loop fashion and relies on significant development resources related to data collection at various operating conditions for accurate calibration.